It now seems obvious that dependence on imported crude oils or residual or distilled fuel oils for electric power generation in the remaining free nations of the world is no longer reasonable, since most of the world's remaining economically recoverable crude oil reserves are in a small area of the Persian Gulf and in the Soviet Union. The Soviet Union and a few small nations can essentially control both availability and price of crude oil and petroleum products, world-wide, beyond some point in the near future. This will be a matter of critical importance so long as the world remains heavily dependent on such fuels for primary energy supplies. Control by these nations seems destined to become more dominant as the remaining reserves of economically recoverable crude oil in other areas of the world are rapidly depleted. It is primarily this situation which makes the development of new, alternative means for electric power generation, which are not dependent on petroleum, so critically important.
Sources of economically recoverable natural gas which can be delivered by pipeline are also declining rapidly in the United States. Most of the world's known reserves of natural gas are in areas where production and delivery by pipelines to conventional markets is not economically feasible, and virtually not even possible.
The maximum use of coal for power generation is now widely advocated, because the resources are so very great. However, there are serious problems involved in greatly increasing the use of coal. If the necessary technologies for economical, long distance coal transportation; for utilization of the lower quality coals; and for adequate environmental controls are developed; the known, mineable coal reserves are sufficient to provide most of the world's energy needs for centuries. By comparison, the known reserves of natural gas which is economically recoverable and deliverable by present means may last only a few decades, and serious shortages may evolve in just a few years. The coal resources are widely distributed throughout much of the world, and many nations, which have little or no crude oil or natural gas resources, have coals or lignites available, and could become relatively self-sufficient from the standpoint of their energy needs. Broadening the energy base for all nations would surely serve to stabilize the economies of nations throughout the World, and stimulate the development of many of the emerging nations.
The present state-of-the-art provides various means for utilizing coal or natural gas as alternatives to fuel oils for generating electric power. Some of these are well known, or conventional, and in wide commercial use, others are in various stages of development. Conventional methods include the pulverized coal-fired steam turbine power plants, and gas-fired steam turbine power plants, (the Rankine cycle power plants). Others are the natural gas-fired, open cycle, gas turbine power plants (Brayton cycle plants), and the more efficient natural gas-fired, combined cycle power plants (Brayton/Rankine cycle plants). Many U. S. utility companies have adopted and promoted the use of gas-fired combined cycle plants, because of their low capital cost and high efficiencies, but many are now expressing concern about becoming committed to deliverable natural gas, which surely will once again become limited in supply and high in cost in the near future. The proven, economically recoverable natural gas reserves were recently estimated at seventeen years supply for the United States, at current rates of use. The prospects for significant new discoveries are not good, and the rate of use is growing.
There are some emerging technologies which may prove useful and beneficial to the utility industry. Two types of coal-fired, fluid-bed combustion boilers are under development, and may be useful, at least in relatively small Rankine cycle power plants. They are quite expensive to build, operate and maintain, and produce large amounts of solid waste which must be disposed of, about comparable in this respect to conventional coal-fired plants with limestone scrubbers. They are capable of substantially reducing sulphur oxides and nitrogen oxides emissions, and can use relatively high sulphur coals.
In recent years, the integrated gasification combined cycle (IGCC) power plants have been developed to burn low-Btu gases produced by coal gasification. These plants are very expensive, but have the advantage that they can burn high-sulphur coals and also meet rather strict air pollution standards for sulphur oxides, nitrogen oxides and particulate emissions. The IGCC power plants require first gasifying the coal, then thoroughly cleaning the gas, then burning it in gas-fired combined cycle power plants (Brayton/Rankine cycle plants). In both of the above cases, for the gas-fired combined cycle (Brayton cycle/Rankine cycle) power plants, some additional fuel may be burned in the heat recovery steam generators of the Rankine cycle portion of the plant. This is called "supplementary firing", and can provide some additional capacity, but with reduced efficiency. It is generally not recommended, because with the high cost of the fuels required for such plants, the drop in efficiency makes it uneconomical.
Fully-fired combined cycle plants have been designed and are now in use in West Germany, and perhaps in other areas. (See Gas and Coal-Fired Combined Cycle Plants, a booklet for presentation at the American Power Conference, Chicago Illinois, Apr. 14-16, 1986, Utility Power Corporation). These plants burn natural gas in the gas turbine generators and use the gas turbine exhaust gases for combustion air for burning coal in conventional pulverized coal-fired steam generators for Rankine cycle power plants. Similar plants, designed to burn natural gas and oil, have been proposed in the United States, and a conceptual design was done for Electric Power Research Institute by Westinghouse Electric Company a few years ago. However, these types of plants do not solve the problems of oil and gas availability and the future escalating costs expected for these fuels. Consequently, they would be high risk investments which might result in very high costs for producing power in the relatively near future. It has been proposed that they could be converted to IGCC plants by adding coal gasification plants, when the cost of natural gas and/or oil becomes too high for their practical use as power plant fuels. These would be a very costly conversions, and dependent on conventional coal delivery and handling methods.
Other technologies have been proposed as improved means for utilizing coal to produce electric power, but appear to have only little potential for commercial use. These include the stabilized coal-oil slurry fuels and coal-water slurry fuels, simulating the fluid characteristics of the stable Methacoal fuels, and proposed to replace heavy or residual fuel oils for oil-fired power plants. It is very questionable whether either of these have any real world potential for commercial development. Residual fuel oil prices in the range of forty dollars or more per barrel are considered necessary by most proponents to justify their commmercial development. Both of these slurry fuels have reportedly increased the ash-fusion problems in the boilers, which may be very difficult to overcome, and which imposes costly and wasteful limits on the quality of coal which can be used. Both may compound the problem of the formation of carcenogenic, ultra-fine, one-tenth micron, particulate emissions of vaporized and re-condensed heavy-metal compounds, already plaguing both coal-fired and residual oil-fired power plants. Ultra-clean and ultra-fine coal is considered a prerequisite for firing of coal-water slurries, and this prices these fuels at levels too high to provide significant profit potentials or incentives for their development.
New developments in these fields, which may lead to commercial utilization, include the improved coal-oil slurry fuels, see U.S. Pat. No. 4,089,657, May 16, 1978, Stabilized Suspension of Carbon in Hydrocarbon Fuel and Method of Preparation). This process uses methanol to improve both rheological characteristics and combustion characteristics of the coal-oil slurry fuels. New developments in coal-water slurry fuels, also using methanol for improving the rheological and combustion characteristics of the slurry fuels, are pending, (see U.S. Pat. Application Ser. No. 185391, Feb. 22, 1988, Stabilized Suspensions of Carbonaceous Fuel Particles in Water), now allowed for issuance.
Magnetohydrodynamics has been under development for several decades with little chance for success. Coal-chemical batteries for direct conversion of coal to electric power have been proposed also, but seem to have limited if any potential.
Conventional coal-fired steam power plants have almost reached the practical limits of expansion in the United States, because of the limitations of siting with respect to coal supply, length of power lines required for transmission of power from mine-mouth plants, transportation difficulties in delivering coal to plants located near the load centers, problems in meeting clean air requirements for exhaust gases, and limits on coal quality which are required for operating the standard types (state-of-the-art) boiler plants now available. The necessary coal quality limits, imposed by design limitations of the power plants, render most of the U. S. coal resources unusable, with today's boiler and combustion designs and exhaust cleaning capabilities. Users must set rigid standards to insure reliable operations, and valuable coal resources must be left unused and are often degraded or wasted by selective mining requirements to meet the imposed standards, or to gain bonuses for high quality. This presents very serious, but generally unrecognized, conservation problems, which are greatly in need of technical and scientific solutions. The present invention contributes greatly to those solutions.
New, patented technologies for providing superior-quality boiler fuels from coal, or from coal and remote natural gas, for use in converted oil-fired type boilers, could allow circumventing many of the problems associated with other coal slurry fuels, but Industry has been slow to adopt their use. These are the unique coal-methanol slurry fuels and the coal-methanol-water slurry fuels herinafter referred to as Methacoal or Methacoal fuels. These fuels actually burn better and provide better performance than residual oils or heavy fuel oils in boilers designed for oil firing. Methacoal fuels (slurries or suspensoids) were developed by one of the present inventors, and patent applications were filed before the more recently popularized development of stabilized coal-oil slurry fuels and coal-water slurry fuels. The development of these later slurry fuels evolved from the development of the Methacoal fuels (coal-alcohol slurry fuels and coal-alcohol-water slurry fuels), from the new rheological and combustion technologies originated and revealed by the developing company, and from the patents cited hereinafter. The potentials for Methacoal boiler fuels development, as replacements for residual and heavy fuel oils, is very great. More than one hundred thousand megawatts of power plant capacity in the United States alone could be converted at savings of tens of billions of dollars to the Utility Industry.
However, even more advantageous means for utilizing coal or lignite and natural gas resources together, or coal or lignite resources alone, delivered as anhydrous or low moisture content Methacoal fuels, are urgently needed. The improved means should be capable of accelerating the development and utilization of these resources, of reducing the exhaust gas pollution levels, of reducing fuel consumption (or heat rates), and of making the remote natural gas resources and the low-quality, high moisture content coal resources, (which are usually also low-sulphur coals or lignites), profitably useful as high-quality power plant fuels. This necessitates the use of the unique, Methacoal-derived liquid and particulate fuels, delivered as Methacoal slurry fuels, then separated at the power plant; and the development of a new type of high efficiency power plant to make optimum use of the unique fuels provided. This makes both the remote natural gas (natural gas which cannot be economically delivered to conventional markets) and distant or remote coals or lignites easily and economically transportable for great distances to the power plant facilities located near the load centers. The present invention provides these means.
The use of natural gas as boiler fuel for gas-fired steam generation plants has been greatly expanded in the United States during the past several years, even though there are estimates indicating only seventeen years of remaining proven reserves, and not very good possibilities of finding significant new reserves which are economically recoverable and transportable by pipeline. Also, gas turbine peaking units and cogeneration plants based on natural gas firing have become popular and widely developed, because they are low-cost and economically attractive for the very short near-term future, while natural gas prices are depressed by low oil prices and temporary surpluses of production capacity.
The United States should be seeking means for effecting conservation of the precious, and non-replenishable, natural gas resources, and for limiting their use to only the most efficient means available. There are now about ten fewer years of natural gas reserves remaining than there was at the time the United States Congress first passed legislation to curtail the wasteful inefficient use of natural gas as fuel for power plant boilers. The very wasteful use of any pipeline deliverable natural gas as boiler fuels should probably again be curtailed, and will have to be at some point in time. The temporary excess of production and delivery capability has apparently misled many into believing that the natural gas resources are virtually undiminishable.
The use of remote and otherwise valueless natural gas for the production of fuel grade methanol, which could then be transported economically to user locations and burned as fuel for combined cycle power plants, gas turbine generators or even as boiler fuel for Rankine cycle power plants, has been proposed many times in the past, and is now again being proposed by some. The economics, however, were never sufficiently attractive for this to be done commercially, even though it would accomplish significant environmental improvements, even compared to burning natural gas.
However, the use of such methanol to process and transport coals or lignites, thereby reducing the costs of transportation for energy derived from the natural gas and also from the solid fuels, and also improving the quality of the coal-derived fuels, provides efficient resource utilization and reasonably low fuel costs. The production, transportation and use of Methacoal fuels can make the use of the remote natural gas resources technically, economically and environmentally feasible for providing fuels to replace residual and heavy fuel oils even at the present "cheap" oil prices.
Even though the potentials for Methacoal fuels development for replacing fuel oils is great indeed, commercial development has been delayed by the large investments required for facilities, and by complacency, fear of change, and fear of the power of either OPEC or Saudi Arabia to lower world oil prices to levels at which no alternative fuels could compete. As an example, when crude oil prices were dropped to under ten dollars per barrel, recently, Methacoal fuels were not sufficiently competitive to encourage would-be investors to fund their development. This is no longer the case.
Conversion of remote natural gas to liquid natural gas (LNG) for transport and then for use as fuel for power generation is too costly, wasteful and dangerous to be practically or economically viable. Obviously, improved new means for more efficient and profitable use of remote natural gas, which is so abundantly and widely distributed throughout much of the world, are also urgently needed. This can have a really beneficial, stabilizing effect on world economics and encourage free trade in ways not susceptible to monopolization.
The present invention, as will be shown, provides practical solutions to many of the existing problems of coal and remote natural gas utilization. It can also provide expanded use of the relatively low sulphur content coals and lignites to gain substantial environmental improvements, while the development of coal cleaning technologies materialize and becomes technically and economically feasible. When the high sulphur content coals can be cleaned sufficiently and economically, to allow their economical use, it may be preferable in many cases to use the cleaned coals as Methacoal fuels in the improved power generation facilities provided by the present invention, instead of relying on current state-of-the-art power generation technologies.
It is desirable that the present invention provide the following features:
1. The invention should provide a new type of coal-based, combined cycle power plant which can be provided by the retrofitting of existing steam-turbine power plants or gas-turbine power plants, or by constructing new, low-capital-cost, fuel-integrated combined cycle power plants, which do not require coal gasifiers, fuel gas cleaning systems, or air reduction oxygen plants for preparation of gaseous fuels, as do the integrated gasification combined cycle power plants.
2. The invention should provide cost effective and energy efficient means for utilizing the unique characteristics and potentials of the coal-methanol slurry fuels, called Methacoal fuels, (see U.S. Pat. No. 4,045,092, Aug. 30, 1977, Fuel Composition and Method of Manufacture), to facilitate the low-cost production and transportation of fluid fuels derived from coals or lignites alone, or derived from coals or lignites and remote or other low-cost natural gas; and should also provide means for utilizing the unique liquid fuels and particulate solid fuels which can be separated from Methacoal fuels, (see U.S. Pat. No. 4,192,651, Mar. 11, 1980, Method of Producing Pulverulent Carbonaceous Fuels).
3. The invention should provide a new type of fuel-integrated, coal-based, combined cycle power plant with heat rates, (or fuel conversion efficiencies), in the same range of, or greater than, those of the natural gas-fired or oil-fired, combined cycle power plants with heat recovery power generation systems, and greater than those of the proposed fully-fired, natural gas and coal-fueled, combined cycle power plants.
4. The invention should provide a new type of coal-based combined cycle power plant which can make possible the efficient and economical use of many low-rank, low-sulphur, high-moisture-content coals and lignites, which either cannot be burned, or can only be burned with great difficulty and low efficiencies, in the state-of-the-art, conventional power plants; because of the low ash fusion temperatures, the ash buildup characteristics, the very high ash content, or the very high moisture content of such fuels.
5. The invention should provide effective and profitable means for developing and utilizing remote natural gas, (which has little if any value for other uses), and oil-associated natural gas resources; which may otherwise be wasted by flaring or left undeveloped because of the very high costs of long-distance pipeline transportation of natural gas or the high costs and safety problems associated with liquid natural gas production, transportation and storage.
6. The invention sould provide a new type of power plant which can achieve significant reductions in sulphur oxides emissions by economically using low or medium sulphur content coals or lignites from distant sources, and by also effecting approximately fifty percent additional reduction in sulphur oxides emissions compared to burning the same low-sulphur coals or lignites in conventional power plants without chemical scrubbers.
7. The invention should provide a new type of power plant for which sites can be selected as optimum with respect to the power load center and the existing power distribution system, and the fuel can be delivered to the plant site from distant coal and lignite resources and remote natural gas resources, and no rail, ship or barge transportation of bulk coal or stockpiling of bulk coal is required.
8. The invention should provide a new type of coal-based power plant which can operate with very low nitrogen oxides levels in the exhaust gases, but without prohibitively expensive chemical scrubbers for nitrogen oxides removal, while incorporating the new technologies for nitrogen oxides reduction, (see U.S. Pat. No. 4,742,784, May, 10, 1988, Methods for Reducing Nitrogen Oxides Emissions from Power Plants Fired by Various Fuels), in addition to the other pollutant reductions described herein.
9. The invention should provide for combustion of the Methacoal-derived pulverized solid fuels with minimum production of the ultrafine, minus one-tenth micron particle-size, (and probably carcinogenic), condensates of heavy metals and heavy metal compounds, which are typically found in great quantity in the exhaust gases from most coal-fired and residual oil-fired power plants. See article by EPRI/DOE researchers, "Size Distribution of Fine Particles from Coal Combustion", Science (AAAS), 1 Jan. 1982, Volume 215, Number 4582.
10. The invention should make possible the use of low-cost, low-pressure, suspensoid pipelines, (Methacoal pipelines), of all sizes, (using low-cost centrifugal pumps); and tanker ships and barges, to replace railroad transportation of coal and long-distance, high-voltage power transmission lines.
11. The invention should provide coal-based power plants of any size at lower capital cost than alternative power generation means, provide for low-cost retrofitting of existing power plants, and provide more economical means for generating and delivering electric power to the consumers, thus benefitting the economies of the geographic areas and the nations where the technologies are utilized.